The present invention includes a gear motor with a fail-safe device consisting of a housing, an electromotor, a reduction gear with at least one planetary gear, an electromagnetic clutch and an output gear shaft, wherein the planetary gear has an internal gear. The internal gear is in mesh with at least one planetary wheel and is fixed in its operation relative to the housing. The planetary gear comprises the electromagnetic clutch, a magnetically conductive armature and a magnetically conductive stator in which an electromagnetic coil is arranged. During the application of current to the electromagnetic coil the internal gear is secured against turning. The term ‘electromagnetic brake’ is also applicable for the term ‘electromagnetic clutch’ which is used frequently in the following description.
From DE 101 17 934 A1 a generic gear motor is known that consists of an electromotor and a reduction gear wherein an internal gear can be coupled and decoupled in its operation by a brake assembly that can be activated electromagnetically in order to manually activate an actuator that is connected to an output gear shaft, in this case a hatchback of a vehicle. In a known gear motor, the electromagnet is arranged radially outside a housing that encloses the reduction gear and can be coupled with the internal gear via an arrangement of levers due to which a considerable construction space and a large number of components are necessary. In addition, the assembly of these components is difficult to some extent. The internal gear of DE 101 17 934 A1 has a large axial length and is supported through an expensive implementation over ball bearings in order to ensure a reliable operation.
Therefore an object of the invention is to provide for reliable operation of the fail-safe device in a gear motor of the aforementioned kind using less construction space and fewer components thus enabling simple assembly.
Another object of the invention is to provide for an internal gear that acts as a magnet armature, is axially displaceable and whose radial outer surface is not a guide surface. Thereby the internal gear may be constructed short without the risk of jamming.
The objects of the present invention are met by providing an internal gear that acts as a magnet armature, is axially displaceable and whose geometric alignment is not determined by the housing at least during a power-on or off condition of the electromagnetic clutch. Since the internal gear itself acts as a magnet armature no additional component is required for this purpose that could be defective and would have to be mounted additionally. The ability for axial displacement of the internal gear allows for a decoupling of the internal gear and the output gear shaft. Since the geometric alignment of the internal gear is not determined by the housing, reliable clutching and declutching is ensured and jamming is safely avoided. The small number of components also economizes on the construction space.
Further forms of the invention are presented in the remainder of the application including the claims. The construction space can be reduced to the extent that the ratio of the axial length of the internal gear to its diameter is smaller than 0.5.